Higher Colonic Tissue Drug Concentrations of Subcutaneous Compared to Intravenous Administration of Infliximab...

Intestinal tissue levels of infliximab (IFX) in patients with inflammatory bowel disease (IBD) treated with subcutaneous (SC) therapy have not been previously assessed.

To compare serum and colonic tissue IFX concentrations in IBD patients receiving SC versus intravenous (IV) IFX.

This observational cross-sectional study included IBD patients on stable SC or IV IFX maintenance therapy undergoing routine follow-up colonoscopy. Clinical activity required elevated CDAI or Mayo score plus ≥ 1 biomarker (fecal calprotectin > 250 μg/g or CRP > 5 mg/L). Blood samples and two colonic biopsies were collected for serum and tissue IFX measurements.

Thirty-five patients were included. Serum and tissue IFX concentrations were significantly higher in the SC versus IV group (22 μg/mL vs. 9 μg/mL, p < 0.001; 25 μg/g vs. 10 μg/g, p = 0.002). Serum and colonic tissue IFX levels were positively correlated in both cohorts (IV: r = 0.42; p = 0.014; SC: r = 0.43; p = 0.001). Colonic tissue IFX concentrations were higher in patients with mild-moderate endoscopic activity than in those without active disease (p < 0.001). Serum and colonic tissue IFX levels both predicted sustained clinical remission, with optimal thresholds of 14.5 μg/mL (p = 0.015) and 17 μg/g (p < 0.005), respectively. Colonic tissue IFX showed higher predictive accuracy (AUROC 0.82, p = 0.01) than serum (AUROC 0.76, p = 0.045).

SC IFX achieved significantly higher serum and colonic tissue concentrations than IV IFX. Colonic tissue IFX levels demonstrated superior clinical relevance and may support future tissue-based therapeutic drug monitoring strategies in IBD.